Method of preparing (3R,4S)-3-acetamido-4-allyl-N-(tert-butyl)pyrrolidine-3-carboxamide

ABSTRACT

A method is provided to conveniently separate racemic (3R,4S)-3-acetamido-4-allyl-N-(tert-butyl)pyrrolidine-3-carboxamide and (3S,4R)-3-acetamido-4-allyl-N-(tert-butyl)pyrrolidine-3-carboxamide using selective crystallization with chiral carboxylic acids.

BACKGROUND

Highly functionalized pyrrolidine based arginase inhibitors have beendescribed in U.S. Patent Publication No. 2017/0121352. For instance,U.S. Patent Publication No. 2017/0121352 describes the synthesis ofpotent arginase inhibitors such as(3R,4S)-1-(L-alanyl)-3-amino-4-(3-boronopropyl)pyrrolidine-3-carboxylicacid. These ring-constrained arginase inhibitors have tremendouspotential as novel therapeutics for a wide variety of diverse diseasessuch as cancer, asthma, cystic fibrosis, myocardial reperfusion injury,sickle cell anemia, erectile dysfunction, and leishmaniasis. Adescription of the role of arginase in these diseases can be found innumerous papers, review articles and patents, including U.S. Pat. No.9,200,011 (Ring constrained analogs as arginase inhibitors), TrendsPharmacol. Sci. 2015, 36(6): 395-405 (“Arginase: an old enzyme with newtricks”), and Clinical and Experimental Immunology 2012, 167: 195-205(“Immunology in the clinic review series; focus on cancer:tumor-associated macrophages: undisputed stars of the inflammatory tumormicroenvironment”).

Although these ring-constrained arginase inhibitors have tremendouspotential as new treatments for various diseases, they contain multiplechiral centers making them inherently complex and challenging to prepareon a commercial scale. Improved methods for making such compounds wouldbe advantageous.

SUMMARY

In some aspects, the present disclosure provides an amine compoundrepresented by formula I:

wherein the variables are defined herein. In specific aspects of thepresent disclosure, the amine compound has an enantiomeric excess (ee)of greater than 75% ee, greater than 80% ee, greater than 85% ee,greater than 90% ee, greater than 95% ee, greater than 97%% ee, greaterthan 98% ee or greater than 99% ee.

In another aspect, the present disclosure provides a salt of an aminecompound represented by formula I and a carboxylic acid compound, suchas that represented by formula A or formula B:

wherein the variables are defined herein.

In certain such embodiments, the disclosure provides crystals of suchamine compounds, crystals of such salts of the amine compounds andcompositions comprising such crystals, especially compositions andcrystals in which the salt is enriched for one diastereomer (i.e., oneenantiomer of the conjugate acid of the amine compound is present inexcess over the other enantiomer, and the conjugate base of thecarboxylic acid compound is present essentially as a single enantiomer(e.g., at least 98% ee)).

In some aspects, the present disclosure provides a method of preparingthe salt by fractional crystallization from a solution, e.g., a solutioncomprising the amine compound (or its conjugate acid) and its enantiomer(e.g., in a racemic mixture or in less than 98% ee of the compound offormula I) and essentially a single enantiomer (e.g., at least 98% ee)of the carboxylic acid compound or its conjugate base. In some aspects,the present disclosure provides methods to prepare the chiral carboxylicacids used in the resolution process and methods to determine theenantiomeric excess of the resolved products using chiral HPLC.

The present disclosure also provides a synthetic process using theaforementioned amine compounds to prepare an arginase inhibitor offormula III:

wherein the variable G is defined herein, and wherein a compound offormula I is an intermediate in the process. In particular embodiments,the compound of formula III has an ee of greater than 75% ee, greaterthan 80% ee, greater than 85% ee, greater than 90% ee, greater than 95%ee, greater than 97%% ee, greater than 98% ee or greater than 99% ee.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows the results of the chiral HPLC analysis for the racemic(syn)-3-acetamido-4-allyl-N-(tert-butyl)-pyrrolidine-3-carboxamideprepared in Example 1.

FIG. 2 shows the results of the chiral HPLC analysis for the crystallineproduct of Example 8.

FIG. 3 shows the results of the chiral HPLC analysis for the crystallineproduct of Example 9.

FIG. 4 shows the results of the chiral HPLC analysis for the crystallineproduct of Example 10.

FIG. 5 shows the results of the chiral HPLC analysis for the crystallineproduct of Example 11.

FIG. 6 shows the results of the chiral HPLC analysis for the crystallineproduct of Example 12.

FIG. 7 shows the results of the chiral HPLC analysis for the crystallineproduct of Example 13.

FIG. 8 shows the results of the chiral HPLC analysis for the crystallineproduct of Example 14.

FIG. 9 shows the results of the chiral HPLC analysis for the crystallineproduct of Example 15.

DETAILED DESCRIPTION

In some aspects, the present disclosure provides an amine compoundrepresented by formula I:

wherein:

-   X is O, S, or NR^(e);-   R^(a) is H, lower alkyl, or lower cycloalkyl;-   R^(b) is —CH₂CH═CH₂, —CH₂CH₂CH₂Z¹, —(CH₂)_(n)C(O)H, or    —(CH₂)_(n)CO₂Z²;-   R^(c) and R^(d) are independently H, lower alkyl, lower cycloalkyl,    silyl, acyl, acyloxy; or R^(c) and R^(d), together with the N that    links them, form an optionally substituted 3- to 6-membered    heteroaryl or heterocyclic ring;-   R^(e) is H or lower alkyl, such as methyl;-   n is 1 or 2;-   Z¹ is a halogen, alkyl sulfonate, aryl sulfonate, or an alkyl    sulfonate optionally substituted with one or more halogen atoms; and-   Z² is H, lower alkyl, or lower cycloalkyl.

In some embodiments, the depicted amine compound of formula I has anenantiomeric excess of greater than 70% ee, 80% ee, 90% ee, 95% ee, 96%ee, 97% ee, 98% ee, 99% ee, or 99.5% ee. In other embodiments, thedepicted amine compound has an enantiomeric excess of at least 90% ee,at least 95% ee, or even 98%, 99%, 99.5% or greater ee. In specificembodiments, the enantiomeric excess of the compound of formula I isbounded by any of the two foregoing embodiments, e.g., an ee rangingfrom 70% to 90%, from 80% to 90%, from 90% to 95%, from 80% to 99.5%,from 90% to 99.5%, from 95% to 99.5%, and so on, and so forth.

In some embodiments, R^(a) is H, C₁₋₄ alkyl, or C₃₋₄ cycloalkyl. In somesuch embodiments, R^(a) is H, methyl, ethyl, propyl, isopropyl,isobutyl, tert-butyl, cyclopropyl, or cyclobutyl. In some particularembodiments, R^(a) is tert-butyl.

In some embodiments, R^(b) is allyl, 3-fluoropropyl, 3-chloropropyl,3-bromopropyl, 3-iodopropyl, 3-propane methanesulfonate, 3-propanetrifluoromethanesulfonate, 3-propane benzenesulfonate, 3-propanepara-tolylsulfonate, acetaldehyde, 3-propionaldehyde, acetic acid,3-propanoic acid, methyl acetate, methyl 3-propanate, ethyl acetate, orethyl 3-propanate. In some particular embodiments, R^(b) is allyl.

In some embodiments, R^(c) is H, C₁₋₄ alkyl, C₃₋₄ cycloalkyl. In somesuch embodiments, R^(c) is H, methyl, ethyl, propyl, isopropyl,isobutyl, sec-butyl, tert-butyl, cyclopropyl, or cyclobutyl. In someparticular embodiments, R^(c) is H.

In some embodiments, R^(d) is a silyl, acyl, or acyloxy group. In somesuch embodiments, R^(d) is trimethylsilyl, triethylsilyl,triisopropylsilyl, tert-butyldimethylsilyl, formyl, acetyl,trifluoroacetyl, propionyl, butanoyl, isobutanoyl, tert-butanoyl,cyclopropanoyl, cyclobutanoyl, benzoyl, methyloxycarbonyl,ethyloxycarbonyl, isopropryloxycarbonyl, tert-butyloxycarbonyl,benzyloxycarbonyl, allyloxycarbonyl, or 9-fluorenylmethyloxycarbonyl. Insome particular embodiments, R^(d) is acetyl or trifluoroacetyl.

In some embodiments, R^(c) and R^(d), together with the N that linksthem, form a heterocyclic or heteroaryl ring. In some such embodiments,R^(c) and R^(d), together with the N that links them, form2,5-dimethylpyrrole, 1H-pyrrole-2,5-dione, pyrrolidine-2,5-dione, orisoindoline-1,3-dione.

In some embodiments, X is O or S.

In some embodiments, X is NR^(e). In some particular embodiments, R^(e)is H.

In some particular embodiments, the amine compound is a compound offormula II:

In some embodiments, the depicted amine compound of formula II has anenantiomeric excess of greater than 70% ee, 80% ee, 90% ee, 95% ee, 96%ee, 97% ee, 98% ee, 99% ee, or 99.5% ee. In other embodiments, thedepicted amine compound has an enantiomeric excess of at least 90% ee,at least 95% ee, or even 98%, 99%, 99.5% or greater ee. In specificembodiments, the enantiomeric excess of the compound of formula II isbounded by any of the two foregoing embodiments, e.g., an ee rangingfrom 70%-90%, from 80%-90%, from 90% to 95%, from 80% to 99.5%, from 90%to 99.5%, from 95% to 99.5%, and so on, and so forth.

In some particular embodiments, the amine compound is a compound offormula IIa:

In some embodiments, the depicted amine compound of formula IIa has anenantiomeric excess of greater than 70% ee, 80% ee, 90% ee, 95% ee, 96%ee, 97% ee, 98% ee, 99% ee, or 99.5% ee. In other embodiments, thedepicted amine compound has an enantiomeric excess of at least 90% ee,at least 95% ee, or even 98%, 99%, 99.5% or greater ee. In specificembodiments, the enantiomeric excess of the compound of formula IIa isbounded by any of the two foregoing embodiments, e.g., an ee rangingfrom 70% to 90%, from 80% to 90%, from 90% to 95%, from 80% to 99.5%,from 90% to 99.5%, from 95% to 99.5%, and so on, and so forth.

In some aspects, the present disclosure provides a salt of an aminecompound represented by formula I and a carboxylic acid compoundrepresented by formula A or B:

wherein:

-   X is O, S, or NR^(e);-   R^(a) is H, lower alkyl, or lower cycloalkyl;-   R^(b) is —CH₂CH═CH₂, —(CH₂)_(n)CH₂Z¹, —(CH₂)_(n)C(O)H, or    —(CH₂)_(n)CO₂Z²;-   R^(c) and R^(d) are independently H, lower alkyl, lower cycloalkyl,    silyl, acyl, acyloxy; or R^(c) and R^(d), together with the N that    links them, form an optionally substituted 3- to 6-membered    heteroaryl or heterocyclic ring;-   R^(e) is H or lower alkyl, such as methyl;-   n is 1 or 2;-   Z¹ is a halogen, alkyl sulfonate, aryl sulfonate, or an alkyl    sulfonate optionally substituted with one or more halogen atoms;-   Z² is H, lower alkyl, or lower cycloalkyl;-   A¹ is phenyl or 5-6 membered heteroaryl, and is optionally    substituted by up to 4 R⁴;-   A² is phenyl or 5-6 membered heteroaryl, and is optionally    substituted by up to 4 R⁵;-   R¹ is lower alkyl or lower cycloalkyl;-   R² and R³ are independently H, lower alkyl, or lower cycloalkyl; or    R² and R³, together with the N that links them, form an optionally    substituted 3- to 6-membered saturated heterocyclic ring optionally    containing 1 or 2 additional heteroatoms selected from S and O; and-   R⁴ and R⁵ are independently halogen, hydroxyl, nitro, lower alkyl,    or lower cycloalkyl.

In some embodiments, the salt is essentially a single enantiomer of asingle diastereomer. In some embodiments, the amine compound in the saltis enantiomerically enriched in the depicted enantiomer, such as greaterthan 70% ee, 80% ee, 90% ee, 95% ee, 96% ee, 97% ee, 98% ee, 99% ee, orat least 99.5% ee.

In some embodiments, R^(a) is H, C₁₋₄ alkyl, or C₃₋₄ cycloalkyl. In somesuch embodiments, R^(a) is H, methyl, ethyl, propyl, isopropyl,isobutyl, tert-butyl, cyclopropyl, or cyclobutyl. In some particularembodiments, R^(a) is tert-butyl.

In some embodiments, R^(b) is allyl, 3-fluoropropyl, 3-chloropropyl,3-bromopropyl, 3-iodopropyl, 3-propane methanesulfonate, 3-propanetrifluoromethanesulfonate, 3-propane benzenesulfonate, 3-propanepara-tolylsulfonate, acetaldehyde, 3-propionaldehyde, acetic acid,3-propanoic acid, methyl acetate, methyl 3-propanate, ethyl acetate, orethyl 3-propanate. In some particular embodiments, R^(b) is allyl.

In some embodiments, R^(c) is H, C₁₋₄ alkyl, or C₃₋₄ cycloalkyl. In somesuch embodiments, R^(c) is H, methyl, ethyl, propyl, isopropyl,isobutyl, sec-butyl, tert-butyl, cyclopropyl, or cyclobutyl. In someparticular embodiments, R^(c) is H.

In some embodiments, R^(d) is a silyl, acyl, or acyloxy group. In somesuch embodiments, R^(d) is trimethylsilyl, triethylsilyl,triisopropylsilyl, tert-butyldimethylsilyl, formyl, acetyl,trifluoroacetyl, propionyl, butanoyl, isobutanoyl, tert-butanoyl,cyclopropanoyl, cyclobutanoyl, benzoyl, methyloxycarbonyl,ethyloxycarbonyl, isopropryloxycarbonyl, tert-butyloxycarbonyl,benzyloxycarbonyl, allyloxycarbonyl, or 9-fluorenylmethyloxycarbonyl. Insome particular embodiments, R^(d) is acetyl or trifluoroacetyl.

In some embodiments, R^(c) and R^(d), together with the N that linksthem, form a heterocyclic or heteroaryl ring. In some such embodiments,R^(c) and R^(d), together with the N that links them, form2,5-dimethylpyrrole, 1H-pyrrole-2,5-dione, pyrrolidine-2,5-dione, orisoindoline-1,3-dione.

In some embodiments, X is O or S.

In some embodiments, X is NR^(e). In some particular embodiments, R^(e)is H.

In some aspects, the present disclosure provides a salt of an aminecompound represented by formula II and a carboxylic acid compoundrepresented by formula A or B:

wherein:

-   A¹ is phenyl or 5-6 membered heteroaryl, and is optionally    substituted by up to 4 R⁴;-   A² is phenyl or 5-6 membered heteroaryl, and is optionally    substituted by up to 4 R⁵;-   X is O, S, or NR^(e);-   R^(a), R^(b), and R^(f) are independently H, lower alkyl, or lower    cycloalkyl;-   R^(e) is H or lower alkyl, such as methyl;-   R¹ is lower alkyl or lower cycloalkyl;-   R² and R³ are H, lower alkyl, or lower cycloalkyl; or R² and R³,    together with the N that links them, form an optionally substituted    3- to 6-membered saturated heterocyclic ring optionally containing 1    or 2 additional heteroatoms selected from S and O; and-   R⁴ and R⁵ are independently halogen, hydroxyl, nitro, lower alkyl,    or lower cycloalkyl.

In some embodiments, R^(a) is H, C₁₋₄ alkyl, or C₃₋₄ cycloalkyl. In somesuch embodiments, R^(a) is H, methyl, ethyl, propyl, isopropyl,isobutyl, sec-butyl, tert-butyl, cyclopropyl, or cyclobutyl. In someparticular embodiments, R^(a) is tert-butyl.

In some embodiments, R^(c) is H, C₁₋₄ alkyl, or C₃₋₄ cycloalkyl. In somesuch embodiments, R^(c) is H, methyl, ethyl, propyl, isopropyl,isobutyl, sec-butyl, tert-butyl, cyclopropyl, or cyclobutyl. In someparticular embodiments, R^(c) is H.

In some embodiments, R^(b) is H, C₁₋₄ alkyl, or C₃₋₄ cycloalkyl. In somesuch embodiments, R^(f) is H, methyl, ethyl, propyl, isopropyl,isobutyl, sec-butyl, tert-butyl, cyclopropyl, or cyclobutyl. In someparticular embodiments, R^(f) is methyl.

In some embodiments, X is O or S.

In some embodiments, X is NR^(d). In some particular embodiments, R^(d)is H.

In some particular embodiments, the amine portion of the salt is acompound of formula (IIa).

In some embodiments, the salt is essentially a single enantiomer of asingle diastereomer. In some embodiments, the amine compound in the saltis enantiomerically enriched in the depicted enantiomer, such as greaterthan 70% ee, 80% ee, 90% ee, 95% ee, 96% ee, 97% ee, 98% ee, 99% ee, orat least 99.5% ee. In some embodiments, the carboxylic acid compound inthe salt is enantiomerically enriched in the depicted enantiomer, suchas at least 90% ee, at least 95% ee, or even 98%, 99% or greater ee.

In some embodiments, A¹ is phenyl. In some embodiments, A¹ is 5-6membered heteroaryl, such as thiophenyl, furanyl, thiazolyl,isothiazolyl, indazolyl, oxazolyl, isoxazolyl, pyridazinyl, pyrimidyl,pyrazinyl, 1,2,4-triazinyl, 1,2,3-triazinyl, or 1,3,5-triazinyl.

In some embodiments, A² is phenyl. In some embodiments, A² is 5-6membered heteroaryl, such as thiophenyl, furanyl, thiazolyl,isothiazolyl, indazolyl, oxazolyl, isoxazolyl, pyridazinyl, pyrimidyl,pyrazinyl, 1,2,4-triazinyl, 1,2,3-triazinyl, or 1,3,5-triazinyl.

In some embodiments, A¹ and A² are identical. In some embodiments, A¹and A² are different.

In some embodiments, A¹ and A² are both phenyl.

In some embodiments, A¹ is substituted by one R⁴, for example at the 2-,3-, 4-, or 5-position relative to the point of attachment to theremainder of formula B.

In some embodiments, A² is substituted by one R⁵, for example at the 2-,3-, 4-, or 5-position relative to the point of attachment to theremainder of formula B.

In some embodiments, A¹ is substituted by two R⁴, for example at the1,2-; 2,3-; 1,3-; 1,4-; 1,5-; or 2,4-positions relative to the point ofattachment to the remainder of formula B.

In some embodiments, A² is substituted by two R⁵, for example at the1,2-; 2,3-; 1,3-; 1,4-; 1,5-; or 2,4-positions relative to the point ofattachment to the remainder of formula B.

In some embodiments, A¹ and A² are identically substituted. In someembodiments, A¹ and A² are differently substituted.

In some embodiments, the carboxylic acid compound is represented byformula A or formula B-I:

In some embodiments, the carboxylic acid compound is represented byformula A. In some embodiments, R¹ is H, C₁₋₄ alkyl, or C₃₋₄ cycloalkyl.In some embodiments, R¹ is methyl, ethyl, propyl, isopropyl, isobutyl,sec-butyl, tert-butyl, cyclopropyl, or cyclobutyl. In some particularembodiments, R¹ is methyl.

In some embodiments, the carboxylic acid compound is represented byformula B. In some particular embodiments, the carboxylic acid compoundis represented by formula B-I.

In some embodiments, R² and R³ are independently H, C₁₋₄ alkyl, or C₃₋₄cycloalkyl; or R² and R³, together with the N that links them, form anN-linked 3- to 6-membered saturated heterocyclic ring. In someparticular embodiments, R² and R³ are independently methyl, ethyl, orisopropyl; or R² and R³, together with the N that links them, form apyrrolidinyl.

In some embodiments, R⁴ is C₁₋₄ alkyl, or C₃₋₄ cycloalkyl. In someembodiments, R⁴ is methyl, ethyl, propyl, isopropyl, isobutyl,sec-butyl, tert-butyl, cyclopropyl, or cyclobutyl. In some particularembodiments, R⁴ is methyl. In other embodiments, R⁴ is halogen,hydroxyl, or nitro. In certain particular embodiments, R⁴ and R⁵ are thesame.

In some embodiments, R⁵ is C₁₋₄ alkyl, or C₃₋₄ cycloalkyl. In someembodiments, R⁵ is H, methyl, ethyl, propyl, isopropyl, isobutyl,sec-butyl, tert-butyl, cyclopropyl, or cyclobutyl. In some particularembodiments, R⁵ is methyl. In other embodiments, R⁵ is halogen,hydroxyl, or nitro.

In some particular embodiments, the carboxylic acid compound is:

In some aspects, the present disclosure provides a method of preparingthe salts provided herein by fractional crystallization from a solution,comprising: preparing a crystallization solution comprising the aminecompound, essentially a single enantiomer of the carboxylic acidcompound, and a solvent; and crystallizing from the crystallizationsolution a salt of the amine compound and the carboxylic acid compound.

In some embodiments, the solvent comprises water, methanol, ethanol,isopropanol, ethyl acetate, or acetonitrile or a mixture of any ofthese. In some embodiments, the solvent is isopropanol. In someembodiments, the solvent is ethyl acetate. In some embodiments, thesolvent is acetonitrile. In some embodiments, the solvent is a mixtureof methanol and ethyl acetate, such as 5-35% methanol/ethyl acetate,preferably 15-25% methanol/ethyl acetate. In some embodiments, thesolvent is a mixture of methanol and isopropanol, such as 5-35%methanol/isopropanol, preferably 5-25% methanol/isopropanol. In someembodiments, the solvent is methanol.

In some embodiments, the crystallization solution comprises the aminecompound and its enantiomer. In some embodiments, the crystallizationsolution comprises a racemic mixture of the amine compound and itsenantiomer. In some embodiments, the crystallization solution comprisesan enantiomeric excess of the amine compound over its enantiomer. Insome such embodiments, the amine compound in the crystallizationsolution is present at less than 5% ee, less than 10% ee, less than 15%ee, less than 20% ee, less than 25% ee, less than 30% ee, less than 40%ee, less than 50% ee, less than 60% ee, less than 70% ee, less than 80%ee, less than 90% ee, less than 95% ee, at least 96% ee, at least 97%ee, at least 98% ee, at least 99% ee, or at least 99.5% ee. In someembodiments, the enantiomer of the amine compound is enriched for oneenantiomer. In some such embodiments, the enantiomer of the aminecompound in the crystallization solution has at least 5% ee, at least10% ee, at least 15% ee, at least 20% ee, at least 25% ee, at least 30%ee, at least 40% ee, at least 50% ee, at least 60% ee, at least 70% ee,at least 80% ee, at least 90% ee, at least 95% ee, at least 96% ee, atleast 97% ee, at least 98% ee, at least 99% ee, or at least 99.5% ee.

In some embodiments, the salt of the amine compound with the carboxylicacid that results from the crystallizing step is essentially a singleenantiomer of a single diastereomer. In some embodiments, the salt ispresent in at least 5% ee, at least 10% ee, at least 15% ee, at least20% ee, at least 25% ee, at least 30% ee, at least 40% ee, at least 50%ee, at least 60% ee, at least 70% ee, at least 80% ee, at least 90% ee,at least 95% ee, at least 96% ee, at least 97% ee, at least 98% ee, atleast 99% ee, or at least 99.5% ee.

In some embodiments, before the desired amine compound is crystallized,the undesired enantiomer is first crystallized using an enantiomer ofone of the carboxylic acid compounds. By performing thispre-crystallization step, the crystallization solution is formed as thesupernatant, and is thereby enriched in the desired amine compoundrelative to the starting solution. Thus, according to certainembodiments, preparing the crystallization solution comprises preparinga precursor solution comprising the amine compound, a second, undesired,enantiomer of the amine compound, and a second enantiomer of thecarboxylic acid compound. That is, the precursor solution comprises theenantiomeric amines of formulas II and II′, and the carboxylic acid ofeither formula A′, B′, or B-I′ (i.e., the carboxylic acid is theopposite enantiomer from that of formula A, B, or B-I):

The variables in formulas II, II′, A′, and B′ may be selected as definedabove with respect to formulas II, A, and B. According to theseembodiments, the second enantiomer of the carboxylic acid compound(i.e., the enantiomer depicted in formula A′, B′, or B-I′) is selectedto crystallize with the undesired enantiomer of the amine compound(i.e., the enantiomer depicted in formula II′). Next, the salt of thesecond enantiomer of the amine compound with the second enantiomer ofthe carboxylic acid compound is crystallized from the precursorsolution, thereby forming the crystallization solution as thesupernatant. It is not necessary that the carboxylic acid used in thepre-crystallization step (i.e., the enantiomer depicted in formula A′,B′, or B-I′) is the opposite enantiomer of the carboxylic acid used inthe crystallization step (i.e., the enantiomer depicted in formula A, B,or B-I). In some embodiments, the carboxylic acid used in thepre-crystallization step is the opposite enantiomer of the carboxylicacid used in the crystallization step. In some embodiments, thecarboxylic acid used in the pre-crystallization step is not astereoisomer of the carboxylic acid used in the crystallization step.

Crystallizing the undesired enantiomer in this way can result in acrystallization solution in which the desired amine compound is presentin at least 5% ee, at least 10% ee, at least 15% ee, at least 20% ee, atleast 25% ee, at least 30% ee, at least 40% ee, at least 50% ee, atleast 60% ee, at least 70% ee, at least 80% ee, at least 90% ee, atleast 95% ee, at least 96% ee, at least 97% ee, at least 98% ee, atleast 99% ee, or at least 99.5% ee. The desired salt can then becrystallized from the crystallization solution as described above.

In some embodiments, the present disclosure provides a method forseparating a mixture of(3R,4S)-3-acetamido-4-allyl-N-(tert-butyl)pyrrolidine-3-carboxamide IIaand (3S,4R)-3-acetamido-4-allyl-N-(tert-butyl)pyrrolidine-3-carboxamideIIb into essentially single enantiomers using selective crystallizationwith chiral carboxylic acids according to formula A or B. Suchcarboxylic acids are commercially available or may be prepared in one ortwo synthetic steps from phthalic anhydride and diacylated tartaric acidor its anhydride, such as (+)-2,3-dibenzoyl-D-tartaric acid,(−)-2,3-dibenzoyl-L-tartaric acid, (+)-O,O′-di-p-toluoyl-D-tartaric acidor (−)-O,O′-di-p-toluoyl-L-tartaric acid.

In a typical procedure, an amine compound such as(3R,4S)-3-acetamido-4-allyl-N-(tert-butyl)pyrrolidine-3-carboxamide IIaand its enantiomer(3S,4R)-3-acetamido-4-allyl-N-(tert-butyl)pyrrolidine-3-carboxamide IIbis dissolved in a suitable solvent or solvent mixture and combined witha second solution containing essentially a single enantiomer of aselected carboxylic acid of formula A or formula B. The amine compoundIIa may be present as a racemic mixture with its enantiomer IIb, it maybe enriched over IIb, or IIb may be enriched over IIa. In someembodiments, IIa is enriched to 5% ee, 10% ee, 15% ee, 20% ee, 25% ee,30% ee, 40% ee, 50% ee, 60% ee, 70% ee, 80% ee, 90% ee, or even 95% orgreater ee. In some embodiments, IIb is enriched to 5% ee, 10% ee, 15%ee, 20% ee, 25% ee, 30% ee, 40% ee, 50% ee, 60% ee, 70% ee, 80% ee, 90%ee, or even 95% or greater ee. The solvents that may be used alone or incombination as solvent mixtures include but are not limited to water,methanol, ethanol, isopropyl alcohol, acetonitrile and ethyl acetate. Insome cases, warming one or both of the solutions may be required tofully dissolve the amine or the carboxylic acid. Once the solutions arecombined, the resulting solution is allowed to stand until the saltformed from the chiral carboxylic acid and substantially one of theamine enantiomers forms a precipitate, the selective crystallization.

The time required for this crystallization process will vary dependingon the specific carboxylic acid, solvents, concentration, andtemperature. In some instances, the precipitate will begin forming inminutes, in others in may take several hours or even days. In general, aslower process will give better enantiomeric selectivity. Thus in someinstances, crystallization conditions that give a slower process arepreferable. These include more polar solvents, less concentratedsolutions and higher temperatures or a slow rate of cooling.

Since the methods described herein use chiral carboxylic acids that arereadily available (commercially or in a few synthetic steps) in eitherenantiomeric form, either enantiomer of the amine can be obtained simplyby using the appropriate enantiomer of the carboxylic acid.

In some cases, a greater yield and/or enantiomeric excess can beobtained by using two sequential crystallizations—the first with oneenantiomer of the carboxylic acid to remove a significant portion of theundesired amine (undesired enantiomer) as the precipitated salt, then asecond crystallization with the second enantiomer of the carboxylic acidto obtain the desired amine as the precipitated salt.

Although numerous carboxylic acids of formula A and formula B may beused as disclosed herein, certain particular carboxylic acids includethose illustrated and named below as compounds 3-8 in Table 1.

Compound Structure Name 3

(R)-2-((1- phenylethyl)carbamoyl)benzoic acid 4

(2S,3S)-2,3-bis(benzoyloxy)-4- (dimethylamino)-4-oxobutanoic acid 5

(2S,3S)-2,3-bis(benzoyloxy)-4- (diethylamino)-4-oxobutanoic acid 6

(2S,3S)-2,3-bis(benzoyloxy)-4-oxo- 4-(pyrrolidin-1-yl)butanoic acid 7

(2S,3S)-2,3-bis(benzoyloxy)-4- (isopropylamino)-4-oxobutanoic acid 8

(3S,4S)-5-(isopropylamino)-3,4- bis((4-methylbenzoyl)oxy)-2,5-dioxopentanoic acid

The starting materials and reagents used in the preparation of thecompounds in the present disclosure are either available from commercialsuppliers such as Sigma-Aldrich (St. Louis, Mo.) or Fisher Scientific(Hampton, N.H.) or are prepared by methods known to those skilled in theart following procedures set forth in references such as Fieser andFieser's Reagents for Organic Synthesis, Volumes 1-17 (John Wiley andSons, 1991), Organic Reactions, Volumes 1-40 (John Wiley and Sons,1991), and March's Advanced Organic Chemistry (John Wiley and Sons,4^(th) Edition). The schemes provided herein are merely illustrative ofsome methods by which the compounds of the present disclosure can besynthesized, and various modifications of these schemes can be made andsuggested by those skilled in the art having referred to thisdisclosure. The starting materials, intermediates, and final products ofthe reaction may be isolated and purified using conventional techniques,including but limited to filtration, distillation, crystallization,chromatography and the like.

The present disclosure also provides a synthetic process to prepare anarginase inhibitor of formula III:

wherein G of arginase inhibitor III is an amino acid side chain, such ashydrogen (glycine), methyl (alanine), isopropyl (valine), sec-butyl(isoleucine), —CH₂CH(CH₃)₂ (leucine), benzyl (phenylalanine),p-hydroxybenzyl (tyrosine), —CH₂OH (serine), —CH(OH)CH₃ (threonine),—CH₂-3-indoyl (tryptophan), —CH₂COOH (aspartic acid), —CH₂CH₂COOH(glutamic acid), —CH₂C(O)NH₂ (asparagine), —CH₂CH₂C(O)NH₂ (glutamine),—CH₂SH (cysteine), —CH₂CH₂SCH₃ (methionine), —(CH₂)₄NH₂ (lysine),—(CH₂)₃NHC(═NH)NH₂ (arginine) or —CH₂-3-imidazoyl (histidine).

In particular embodiments, G is methyl. In other particular embodiments,G is hydrogen. In other particular embodiments, G is —CH₂OH.

In particular embodiments, the compound of formula III obtained by theprocesses described here has an enantiomeric excess of greater than 80%,90% ee, 95% ee, 96% ee, 97% ee, 98% ee, 99% ee, or even greater than99.5% ee.

In accordance with the disclosure, the arginase inhibitor of generalformula III can be prepared by using a compound of formula I, formula IIor formula IIa as an intermediate. A general schematic for synthesizinga compound of formula III from a compound of formula I is depicted inScheme A. In Scheme A, the multiple arrows represent multiple syntheticsteps, which will be described in more detail below.

In some aspects, arginase inhibitors of general formula III can beprepared as illustrated and described in the general Scheme B below.

Epoxide 11 can be obtained commercially or prepared by epoxidation oftert-butyl 2,5-dihydro-1H-pyrrole-1-carboxylate, for example from thereaction with aqueous N-bromosuccinimide or meta-chloroperoxybenzoicacid. Allylation of epoxide 11 to form racemic alcohol 12 can beaccomplished using an appropriate allyl metal nucleophile, such as anallyl lithium reagent, an ally magnesium reagent, an allyl zinc reagent,an allyl copper reagent, or reagents including mixtures of these metals.The epoxide ring opening may also be assisted with Lewis acids ortransitional metals. Solvents can include any of those suitable fornucleophilic addition, such as but limited to diethyl ether,tetrahydrofuran, 2-methyltetrahydrofuran, and the like. Racemic alcohol12 can then be oxidized to ketone 13 using known methods readilyapparent to those skill in the art for secondary alcohols, such as butnot limited to, Swern oxidation, Parikh-Doering oxidation, Corey-Kimoxidation, oxidation using hypervalent iodine, and the like. Ketone 13can then be transformed in a multi-component reaction to racemic aminoacid derivative 14. Such multi-component reactions can include but arenot limited to, the Ugi reaction, the Strecker reaction, and variationsthereof. Variations of solvent, addition sequences, and additives mayalso be employed in these reactions, for example the Ugi reaction can beperformed in range of solvents such as but not limited to,trifluoroethanol, methanol, water, acetonitrile, dichloromethane,tetrahydrofuran, and mixtures thereof, and include additives such asammonium hydroxide. Racemic amino acid derivation 14 can then bedeprotected under readily available conditions (e.g., removal of Bocwith TFA, HCl, or a Lewis acid), treated with DOWEX-550 hydroxide resinor slurried in an appropriate solvent (e.g., methyl tert-butyl ether)and filtered, to afford racemic amine (enantiomer IIa and enantiomerIIb). The racemic amine (IIa and IIb) can then be resolved according tothe methods of the present disclosure to obtain chiral amine IIa. Insome aspects, neutralization of the formed salt, for example using abase such as sodium bicarbonate, sodium carbonate, potassiumbicarbonate, sodium methoxide, etc., can liberate the free amine fromthe salt to allow isolation of chiral amine IIa. Protection of chiralamine IIa and subsequent hydroboration can produce pinacol borate 15. Incompound 15, Pg is a protecting group, as defined below. In otheraspects before hydroboration, neutralization and protection can beperformed in a single step using aqueous sodium bicarbonate anddi-tert-butyl dicarbonate. The protected chiral amine can be subjectedto further enantio-enrichment steps, such as by warm slurry in ethylacetate and n-heptane mixtures and filtration after cooling.Hydroboration can be accomplished using known methods readily apparentto those skill in the art, such as using pinacol borane orbis(pinacolato)diboron in the present of an appropriate iridium orrhodium catalyst. A subsequent selective deprotection/amidation sequencefollowed by global deprotection can afford arginase inhibitorrepresented by formula III.

In certain aspects, the compounds of the present disclosure can beprepared using the methods illustrated in Schemes C and D below, and inthe more detailed procedures described in the examples section. Racemictert-butyl-trans-3-allyl-4-hydroxypyrrolidine-1-carboxylate (IIa andIIb) is prepared from commercially available epoxide 11 in four steps asoutlined in Scheme C. Addition of allyl magnesium bromide in diethylether at 0° C. gives racemic alcohol 12, which after oxidation withsulfur trioxide pyridine complex and DMSO gives the corresponding ketone13. Subsequent treatment with ammonium acetate and tert-butyl isocyanidein methanol at 0° C. gives the racemic amino acid derivative 14 as amixture of syn- and anti-isomers which are separated by crystallization.Deprotection of the tert-butyl carbamate (Boc group) usingtrifluoroacetic acid in dichloromethane followed by treatment withDOWEX-550 hydroxide resin gives racemic amine (IIa and IIb) as a freebase.

The method for resolving the racemic amine (IIa and IIb) into itssubstantially single enantiomers using a chiral carboxylic acid of thedisclosure is illustrated in Scheme D. In this example, racemic(syn)-3-acetamido-4-allyl-N-(tert-butyl)pyrrolidine-3-carboxamide (IIaand IIb) and (R)-2-((1-phenylethyl)carbamoyl)benzoic acid 3 aredissolved in methanol (15%) and ethyl acetate (85%) with warming. Oncethe solution becomes clear, it is allowed to cool and a precipitateslowly forms. The precipitate, which is the salt formed from acid 3, andamine IIa, is separated by filtration. This salt can be free-based usingstandard methods or used directly in the next step of the synthesis.

The methods disclosed herein can be carried out by those generallyskilled in the art of organic synthesis using the detailed experimentalmethods provided herein. It is understood that the process of selectivecrystallization is dependent on many factors including the choice ofsolvent(s), temperature, concentration and the amount of the chiralcarboxylic acid present. The specific choice of these variables willdetermine the results of the crystallization and may be modifieddepending on the desired outcome (yield, enantiomeric excess,concentration, time, cost). For example, a more dilute crystallizationsolution will typically facilitate slower crystallization, oftenimproving enantioselectivity, but with lower recovery; while a moreconcentrated solution will often accelerate the crystallization process,providing a higher yield but with a somewhat lower enantiomeric excess.Seed crystals of the desired material also will generally facilitate thecrystallization process.

Definitions

The term “acyl” is art-recognized and refers to a group represented bythe general formula hydrocarbylC(O)—, preferably alkylC(O)—.

The term “acylamino” is art-recognized and refers to an amino groupsubstituted with an acyl group and may be represented, for example, bythe formula hydrocarbylC(O)NH—.

The term “acyloxy” is art-recognized and refers to a group representedby the general formula hydrocarbylC(O)O—, preferably alkylC(O)O—.

The term “alkoxy” refers to an alkyl group, preferably a lower alkylgroup, having an oxygen attached thereto. Representative alkoxy groupsinclude methoxy, trifluoromethoxy, ethoxy, propoxy, tert-butoxy and thelike.

The term “alkoxyalkyl” refers to an alkyl group substituted with analkoxy group and may be represented by the general formulaalkyl-O-alkyl.

The term “alkenyl”, as used herein, refers to an aliphatic groupcontaining at least one double bond and is intended to include both“unsubstituted alkenyls” and “substituted alkenyls”, the latter of whichrefers to alkenyl moieties having substituents replacing a hydrogen onone or more carbons of the alkenyl group. Such substituents may occur onone or more carbons that are included or not included in one or moredouble bonds. Moreover, such substituents include all those contemplatedfor alkyl groups, as discussed below, except where stability isprohibitive. For example, substitution of alkenyl groups by one or morealkyl, carbocyclyl, aryl, heterocyclyl, or heteroaryl groups iscontemplated.

An “alkyl” group or “alkane” is a straight chained or branchednon-aromatic hydrocarbon which is completely saturated. Typically, astraight chained or branched alkyl group has from 1 to about 20 carbonatoms, preferably from 1 to about 10, more preferably from 1 to about 6unless otherwise defined. Examples of straight chained and branchedalkyl groups include methyl, ethyl, n-propyl, iso-propyl, n-butyl,sec-butyl, tert-butyl, pentyl, hexyl, pentyl and octyl. A C₁-C₆ straightchained or branched alkyl group is also referred to as a “lower alkyl”group.

Moreover, the term “alkyl” (or “lower alkyl”) as used throughout thespecification, examples, and claims is intended to include both“unsubstituted alkyls” and “substituted alkyls”, the latter of whichrefers to alkyl moieties having substituents replacing a hydrogen on oneor more carbons of the hydrocarbon backbone. Such substituents, if nototherwise specified, can include, for example, a halogen (e.g., fluoro),a hydroxyl, an alkoxy, a cyano, a nitro, an azido, a sulfhydryl, analkylthio, a heterocyclyl, an aralkyl, or an aromatic or heteroaromaticmoiety. In particular embodiments, the substituents on substitutedalkyls are selected from C₁₋₆ alkyl, C₃₋₆ cycloalkyl, halogen, cyano, orhydroxyl. In more particular embodiments, the substituents onsubstituted alkyls are selected from fluoro, cyano, or hydroxyl. It willbe understood by those skilled in the art that the moieties substitutedon the hydrocarbon chain can themselves be substituted, if appropriate.For instance, the substituents of a substituted alkyl may includesubstituted and unsubstituted forms of azido, imino, as well as ethers,alkylthios, —CF₃, —CN and the like. Exemplary substituted alkyls aredescribed below. Cycloalkyls can be further substituted with alkyls,alkenyls, alkoxys, alkylthios, —CF₃, —CN, and the like.

The term “C_(x-y)” when used in conjunction with a chemical moiety, suchas, acyl, acyloxy, alkyl, alkenyl, alkynyl, or alkoxy is meant toinclude groups that contain from x to y carbons in the chain. Forexample, the term “C_(x-y) alkyl” refers to substituted or unsubstitutedsaturated hydrocarbon groups, including straight-chain alkyl andbranched-chain alkyl groups that contain from x to y carbons in thechain, including haloalkyl groups. Particular haloalkyl groups includetrifluoromethyl, difluoromethyl, 2,2,2-trifluoroethyl, andpentafluoroethyl. C₀ alkyl indicates a hydrogen where the group is in aterminal position, a bond if internal. The terms “C_(2-y) alkenyl” and“C_(2-y) alkynyl” refer to substituted or unsubstituted unsaturatedaliphatic groups analogous in length and possible substitution to thealkyls described above, but that contain at least one double or triplebond respectively.

The term “alkylamino”, as used herein, refers to an amino groupsubstituted with at least one alkyl group.

The term “alkylthio”, as used herein, refers to a thiol groupsubstituted with an alkyl group and may be represented by the generalformula alkylS—.

The term “alkynyl”, as used herein, refers to an aliphatic groupcontaining at least one triple bond and is intended to include both“unsubstituted alkynyls” and “substituted alkynyls”, the latter of whichrefers to alkynyl moieties having substituents replacing a hydrogen onone or more carbons of the alkynyl group. Such substituents may occur onone or more carbons that are included or not included in one or moretriple bonds. Moreover, such substituents include all those contemplatedfor alkyl groups, as discussed above, except where stability isprohibitive. For example, substitution of alkynyl groups by one or morealkyl, carbocyclyl, aryl, heterocyclyl, or heteroaryl groups iscontemplated.

The term “amide”, as used herein, refers to a group

wherein each R^(A) independently represent a hydrogen or hydrocarbylgroup, or two R^(A) are taken together with the N atom to which they areattached complete a heterocycle having from 4 to 8 atoms in the ringstructure.

The terms “amine” and “amino” are art-recognized and refer to bothunsubstituted and substituted amines and salts thereof, e.g., a moietythat can be represented by

wherein each R^(A) independently represents a hydrogen or a hydrocarbylgroup, or two R^(A) are taken together with the N atom to which they areattached complete a heterocycle having from 4 to 8 atoms in the ringstructure.

The term “aminoalkyl”, as used herein, refers to an alkyl groupsubstituted with an amino group.

The term “aralkyl”, as used herein, refers to an alkyl group substitutedwith an aryl group.

The term “aryl” as used herein include substituted or unsubstitutedsingle-ring aromatic groups in which each atom of the ring is carbon.Preferably the ring is a 6- or 10-membered ring, more preferably a6-membered ring. The term “aryl” also includes polycyclic ring systemshaving two or more cyclic rings in which two or more carbons are commonto two adjoining rings wherein at least one of the rings is aromatic,e.g., the other cyclic rings can be cycloalkyls, cycloalkenyls,cycloalkynyls, aryls, heteroaryls, and/or heterocyclyls. Aryl groupsinclude benzene, naphthalene, phenanthrene, phenol, aniline, and thelike.

The term “carbamate” is art-recognized and refers to a group

wherein each R^(A) independently represent hydrogen or a hydrocarbylgroup, such as an alkyl group, or both R^(A) taken together with theintervening atom(s) complete a heterocycle having from 4 to 8 atoms inthe ring structure.

The terms “carbocycle”, and “carbocyclic”, as used herein, refers to asaturated or unsaturated ring in which each atom of the ring is carbon.The term carbocycle includes both aromatic carbocycles and non-aromaticcarbocycles. Non-aromatic carbocycles include both cycloalkane rings, inwhich all carbon atoms are saturated, and cycloalkene rings, whichcontain at least one double bond. “Carbocycle” includes 3-8 memberedmonocyclic and 8-12 membered bicyclic rings. Each ring of a bicycliccarbocycle may be selected from saturated, unsaturated and aromaticrings. Carbocycle includes bicyclic molecules in which one, two or threeor more atoms are shared between the two rings. The term “fusedcarbocycle” refers to a bicyclic carbocycle in which each of the ringsshares two adjacent atoms with the other ring. Each ring of a fusedcarbocycle may be selected from saturated, unsaturated and aromaticrings. In an exemplary embodiment, an aromatic ring, e.g., phenyl, maybe fused to a saturated or unsaturated ring, e.g., cyclohexane,cyclopentane, or cyclohexene. Any combination of saturated, unsaturatedand aromatic bicyclic rings, as valence permits, is included in thedefinition of carbocyclic. Exemplary “carbocycles” include cyclopentane,cyclohexane, bicyclo[2.2.1]heptane, 1,5-cyclooctadiene,1,2,3,4-tetrahydronaphthalene, bicyclo[4.2.0]oct-3-ene, naphthalene andadamantane. Exemplary fused carbocycles include decalin, naphthalene,1,2,3,4-tetrahydronaphthalene, bicyclo[4.2.0]octane,4,5,6,7-tetrahydro-1H-indene and bicyclo[4.1.0]hept-3-ene. “Carbocycles”may be substituted at any one or more positions capable of bearing ahydrogen atom.

A “cycloalkyl” group is a cyclic hydrocarbon which is completelysaturated. “Cycloalkyl” includes monocyclic and bicyclic rings.Typically, a monocyclic cycloalkyl group has from 3 to about 10 carbonatoms, more typically 3 to 8 carbon atoms unless otherwise defined. Thesecond ring of a bicyclic cycloalkyl may be selected from saturated,unsaturated, and aromatic rings. Cycloalkyl includes bicyclic moleculesin which one, two or three or more atoms are shared between the tworings. The term “fused cycloalkyl” refers to a bicyclic cycloalkyl inwhich each of the rings shares two adjacent atoms with the other ring.The second ring of a fused bicyclic cycloalkyl may be selected fromsaturated, unsaturated, and aromatic rings. A “cycloalkenyl” group is acyclic hydrocarbon containing one or more double bonds.

The term “carbocyclylalkyl”, as used herein, refers to an alkyl groupsubstituted with a carbocycle group.

The term “carbonate” is art-recognized and refers to a group—OCO₂—R^(A), wherein R^(A) represents a hydrocarbyl group.

The term “carboxy”, as used herein, refers to a group represented by theformula —CO₂H.

The term “ester”, as used herein, refers to a group —C(O)OR^(A) whereinR^(A) represents a hydrocarbyl group.

The term “ether”, as used herein, refers to a hydrocarbyl group linkedthrough an oxygen to another hydrocarbyl group. Accordingly, an ethersubstituent of a hydrocarbyl group may be hydrocarbyl-O—. Ethers may beeither symmetrical or unsymmetrical. Examples of ethers include, but arenot limited to, heterocycle-O-heterocycle and aryl-O-heterocycle. Ethersinclude “alkoxyalkyl” groups, which may be represented by the generalformula alkyl-O-alkyl.

The terms “halo” and “halogen” as used herein means halogen and includeschloro, fluoro, bromo, and iodo.

The terms “hetaralkyl” and “heteroaralkyl”, as used herein, refers to analkyl group substituted with a hetaryl group.

The term “heteroalkyl”, as used herein, refers to a saturated orunsaturated chain of carbon atoms and at least one heteroatom, whereinno two heteroatoms are adjacent.

The terms “heteroaryl” and “hetaryl” include substituted orunsubstituted aromatic single ring structures, preferably 5- to7-membered rings, more preferably 5- to 6-membered rings, whose ringstructures include at least one heteroatom, preferably one to fourheteroatoms, more preferably one or two heteroatoms. The terms“heteroaryl” and “hetaryl” also include polycyclic ring systems havingtwo or more cyclic rings in which two or more carbons are common to twoadjoining rings wherein at least one of the rings is heteroaromatic,e.g., the other cyclic rings can be cycloalkyls, cycloalkenyls,cycloalkynyls, aryls, heteroaryls, and/or heterocyclyls. Heteroarylgroups include, for example, pyrrole, furan, thiophene, imidazole,oxazole, thiazole, pyrazole, pyridine, pyrazine, pyridazine, andpyrimidine, and the like.

The term “heteroatom” as used herein means an atom of any element otherthan carbon or hydrogen. Particular heteroatoms are nitrogen, oxygen,and sulfur.

The terms “heterocyclyl”, “heterocycle”, and “heterocyclic” refer tosubstituted or unsubstituted non-aromatic ring structures, preferably 3-to 10-membered rings, more preferably 3- to 7-membered rings, whose ringstructures include at least one heteroatom, preferably one to fourheteroatoms, more preferably one or two heteroatoms. The terms“heterocyclyl” and “heterocyclic” also include polycyclic ring systemshaving two or more cyclic rings in which two or more carbons are commonto two adjoining rings wherein at least one of the rings isheterocyclic, e.g., the other cyclic rings can be cycloalkyls,cycloalkenyls, cycloalkynyls, aryls, heteroaryls, and/or heterocyclyls.Heterocyclyl groups include, for example, piperidine, piperazine,pyrrolidine, tetrahydropyran, tetrahydrofuran, morpholine, lactones,lactams, and the like.

The term “heterocyclylalkyl”, as used herein, refers to an alkyl groupsubstituted with a heterocycle group.

The term “hydrocarbyl”, as used herein, refers to a group that is bondedthrough a carbon atom that does not have a ═O or ═S substituent, andtypically has at least one carbon-hydrogen bond and a primarily carbonbackbone, but may optionally include heteroatoms. Thus, groups likemethyl, ethoxyethyl, 2-pyridyl, and trifluoromethyl are considered to behydrocarbyl for the purposes of this application, but substituents suchas acetyl (which has a ═O substituent on the linking carbon) and ethoxy(which is linked through oxygen, not carbon) are not. Hydrocarbyl groupsinclude, but are not limited to aryl, heteroaryl, carbocycle,heterocyclyl, alkyl, alkenyl, alkynyl, and combinations thereof.

The term “hydroxyalkyl”, as used herein, refers to an alkyl groupsubstituted with a hydroxy group.

The term “lower” when used in conjunction with a chemical moiety, suchas, acyl, acyloxy, alkyl, alkenyl, alkynyl, alkoxy, or cycloalkyl ismeant to include groups where there are ten or fewer non-hydrogen atomsin the substituent, preferably six or fewer. A “lower alkyl”, forexample, refers to an alkyl group that contains ten or fewer carbonatoms, preferably six or fewer. In certain embodiments, acyl, acyloxy,alkyl, alkenyl, alkynyl, or alkoxy substituents defined herein arerespectively lower acyl, lower acyloxy, lower alkyl, lower alkenyl,lower alkynyl, or lower alkoxy, whether they appear alone or incombination with other substituents, such as in the recitationshydroxyalkyl and aralkyl (in which case, for example, the atoms withinthe aryl group are not counted when counting the carbon atoms in thealkyl substituent).

The terms “polycyclyl”, “polycycle”, and “polycyclic” refer to two ormore rings (e.g., cycloalkyls, cycloalkenyls, cycloalkynyls, aryls,heteroaryls, and/or heterocyclyls) in which two or more atoms are commonto two adjoining rings, e.g., the rings are “fused rings”. Each of therings of the polycycle can be substituted or unsubstituted. In certainembodiments, each ring of the polycycle contains from 3 to 10 atoms inthe ring, preferably from 5 to 7.

The term “silyl” refers to a silicon moiety with three hydrocarbylmoieties attached thereto.

The term “substituted” refers to moieties having substituents replacinga hydrogen on one or more carbons of the backbone. It will be understoodthat “substitution” or “substituted with” includes the implicit provisothat such substitution is in accordance with permitted valence of thesubstituted atom and the substituent, and that the substitution resultsin a stable compound, e.g., which does not spontaneously undergotransformation such as by rearrangement, cyclization, elimination, etc.As used herein, the term “substituted” is contemplated to include allpermissible substituents of organic compounds. In a broad aspect, thepermissible substituents include acyclic and cyclic, branched andunbranched, carbocyclic and heterocyclic, aromatic and non-aromaticsubstituents of organic compounds. The permissible substituents can beone or more and the same or different for appropriate organic compounds.For purposes of this disclosure, the heteroatoms such as nitrogen mayhave hydrogen substituents and/or any permissible substituents oforganic compounds described herein which satisfy the valences of theheteroatoms. Substituents can include any substituents described herein,for example, a halogen, a hydroxyl, an alkoxy, a cyano, a nitro, anazido, a sulfhydryl, an alkylthio, a heterocyclyl, an aralkyl, or anaromatic or heteroaromatic moiety. In particular embodiments, thesubstituents on substituted alkyls are selected from C₁₋₆ alkyl, C₃₋₆cycloalkyl, halogen, cyano, or hydroxyl. In more particular embodiments,the substituents on substituted alkyls are selected from fluoro, cyano,or hydroxyl. It will be understood by those skilled in the art thatsubstituents can themselves be substituted, if appropriate. Unlessspecifically stated as “unsubstituted,” references to chemical moietiesherein are understood to include substituted variants. For example,reference to an “aryl” group or moiety implicitly includes bothsubstituted and unsubstituted variants.

The term “sulfate” is art-recognized and refers to the group —OSO₃H, ora pharmaceutically acceptable salt thereof.

The term “sulfonamide” is art-recognized and refers to the grouprepresented by the general formulae

wherein each R^(A) independently represents hydrogen or hydrocarbyl,such as alkyl, or both R^(A) taken together with the intervening atom(s)complete a heterocycle having from 4 to 8 atoms in the ring structure.

The term “sulfoxide” is art-recognized and refers to the group—S(O)—R^(A), wherein R^(A) represents a hydrocarbyl.

The term “sulfonate” is art-recognized and refers to the group SO₃H, ora pharmaceutically acceptable salt thereof.

The term “sulfone” is art-recognized and refers to the group—S(O)₂—R^(A), wherein R^(A) represents a hydrocarbyl.

The term “thioalkyl”, as used herein, refers to an alkyl groupsubstituted with a thiol group.

The term “thioester”, as used herein, refers to a group —C(O)SR^(A) or—SC(O)R^(A) wherein R^(A) represents a hydrocarbyl.

The term “thioether”, as used herein, is equivalent to an ether, whereinthe oxygen is replaced with a sulfur.

The term “urea” is art-recognized and may be represented by the generalformula

wherein each R^(A) independently represents hydrogen or a hydrocarbyl,such as alkyl, or any occurrence of R^(A) taken together with anotherand the intervening atom(s) complete a heterocycle having from 4 to 8atoms in the ring structure.

“Protecting group” (“Pg”) refers to a group of atoms that, when attachedto a reactive functional group in a molecule, mask, reduce or preventthe reactivity of the functional group. Typically, a protecting groupmay be selectively removed as desired during the course of a synthesis.Examples of protecting groups can be found in Greene and Wuts,Protective Groups in Organic Chemistry, 3^(rd) Ed., 1999, John Wiley &Sons, N.Y. and Harrison et al., Compendium of Synthetic Organic Methods,Vols. 1-8, 1971-1996, John Wiley & Sons, N.Y. Representative nitrogenprotecting groups (Pg) include, but are not limited to, formyl, acetyl,trifluoroacetyl, benzyl, methoxymethyl (“MOM”), benzyloxycarbonyl(“CBZ”), tert-butoxycarbonyl (“Boc”), trimethylsilyl (“TMS”),2-trimethylsilyl-ethanesulfonyl (“2-TES”), triethylsilyl (“TES”),triisopropylsilyl (“TIPS”), tert-butyldimethylsilyltrityl (“TBDMS”) andsubstituted trityl groups, allyloxycarbonyl,9-fluorenylmethyloxycarbonyl (“FMOC”), nitro-veratryloxycarbonyl(“NVOC”) and the like. Representative hydroxyl protecting groupsinclude, but are not limited to, those where the hydroxyl group iseither acylated (esterified) or alkylated such as benzyl and tritylethers, as well as alkyl ethers, tetrahydropyranyl ethers, trialkylsilylethers (e.g., TMS or TIPS groups), glycol ethers, such as ethyleneglycol and propylene glycol derivatives and allyl ethers.

The term “essentially a single enantiomer” refers to a compound that ispresent in greater than 90% enantiomeric excess, such as greater than95%, greater than 96% ee, greater than 97% ee, greater than 98% ee, orgreater than 99% ee.

EXAMPLES

The present application now being generally described, it will be morereadily understood by reference to the following examples which areincluded merely for purposes of illustration of certain aspects andembodiments of the present disclosure, and are not intended to limit theclaimed invention.

For the examples provided below, the enantiomeric excess is determinedafter the basic amine,(syn)-3-acetamido-4-allyl-N-(tert-butyl)pyrrolidine-3-carboxamide fromthe crystalized salt is derivatized as its tert-butyl carbamate or Bocgroup. This product is analyzed by chiral HPLC using a Chiralpak IB 5 μm(4.6 mm×250 mm) column. The specific details for preparation of theBoc-derivative and HPLC analysis are provided below as Examples 16 and17 respectively.

Example 1(syn)-3-acetamido-4-allyl-N-(tert-butyl)pyrrolidine-3-carboxamide (IIaand IIb)

Step 1: Synthesis of Racemictert-butyl-trans-3-allyl-4-hydroxypyrrolidine-1-carboxylate

Allyl magnesium bromide (1,037 mL, 713 mmol, 0.69 M in diethyl ether)was cooled to 0° C. and carefully treated with tert-butyl6-oxa-3-azabicyclo[3.1.0]hexane-3-carboxylate (11, 60 g, 323.9 mmol) inanhydrous diethyl ether (324 mL, 1 M). After the addition was complete,the reaction mixture was stirred for 15 min, slowly quenched withsaturated aqueous ammonium chloride (500 mL), extracted with diethylether (2×400 mL), dried over MgSO₄, filtered, and concentrated.Purification by flash column chromatography (20-40% ethyl acetate inheptane) gavetert-butyl-trans-3-allyl-4-hydroxypyrrolidine-1-carboxylate (12, 64.33g, 87% yield) as a pale yellow oil. ¹H-NMR (CDCl₃, 400 MHz): δ 5.80 (1H,m), 5.06 (2H, m), 4.07 (1H, m), 3.57 (2H, m), 3.22 (1H, m), 3.08 (1H,m), 2.26-2.10 (2H, m) and 1.45 (9H, s).

Step 2: Synthesis of Racemictert-Butyl-3-allyl-4-oxopyrrolidine-1-carboxylate

While under an atmosphere of dry nitrogen, an ice-cooled solution oftert-butyl-trans-3-allyl-4-hydroxypyrrolidine-1-carboxylate (12, 60 g,264 mmol) and diisopropylethylamine (132.2 mL, 799.8 mmol) indichloromethane (750 mL, 0.35 M) was treated dropwise with a solution ofsulfur trioxide pyridine complex (94.95 g, 596.6 mmol) in anhydrous DMSO(750 mL) at a rate to keep the reaction mixture below 10° C. After theaddition was complete, the mixture was stirred at 3° C. for 15 min,quenched with water (380 mL) and extracted with ethyl acetate (500 mL,then 2×300 mL). The combined organic solution was washed twice withwater (200 mL), once with saturated aqueous sodium chloride (200 mL),dried (MgSO₄) and concentrated. The resulting crude oil was distilled at105° C. (0.4 mm Hg) to afford racemic tert-butyl3-allyl-4-oxopyrrolidine-1-carboxylate (13, 58 g, 83% yield) as acolorless oil. ¹H-NMR (CDCl₃, 400 MHz): δ_(H): 5.74 (1H, m), 5.09 (2H,m), 4.02 (1H, m), 3.88 (1H, d, J=19.4 Hz), 3.68 (1H, d, J=19.4 Hz), 3.31(1H, dd, J=9.4, 8.3 Hz), 2.65 (1H, m), 2.54 (1H, m), 2.18 (1H, m) and1.45 (9H, s).

Step 3: Synthesis of Racemic (syn)tert-butyl-3-acetamido-4-allyl-3-(tert-butylcarbamoyl)pyrrolidine-1-carboxylate

While under an atmosphere of dry nitrogen, a solution of ketone (13,79.3 g, 352 mmol) and ammonium acetate (135.7 g, 1,759 mmol) in methanol(200 mL) was cooled to 0° C. and treated with tert-butyl isocyanide(80.2 mL, 704 mol) and stirred at room temperature for 48 h. Theresulting slurry was concentrated, diluted with a 1:2 mixture of ethylacetate and water (300 mL). After stirring for 1 h, the precipitate wasfiltered and washed with water (100 mL) and ice-cold ether (2×50 mL) andair dried. The crude product, which is predominately the syn-isomer(about 10:1), was diluted with ethyl acetate (400 mL), isopropyl alcohol(400 mL) and ethanol (2 mL), then warmed to 70° C. After stirring for anadditional 2 h, the solution was allowed to cool to room temperaturewith continued stirring overnight, filtered and washed with ice-cooledether (2×50 mL) and dried in the oven at 60° C. overnight to giveracemic (syn)tert-butyl-3-acetamido-4-allyl-3-(tert-butylcarbamoyl)pyrrolidine-1-carboxylate(14, 82.1 g, 63% yield.) as a white powder.

Step 4: Synthesis of Racemic(syn)-3-acetamido-4-allyl-N-(tert-butyl)pyrrolidine-3-carboxamide

A solution of racemic(syn)-tert-butyl-3-acetamido-4-allyl-3-(tert-butylcarbamoyl)pyrrolidine-1-carboxylate(14, 20.0 g, 54.4 mmol) in dichloromethane (400 mL) was cooled to 0° C.and treated with trifluoroacetic acid (80 mL, 19.8 mmol) dopwise viaaddition funnel. The solution warmed to room temperature and stirreduntil, no starting material remained as indicated by TLC (about 1 h).The solution was concentrated, re-dissolved in toluene (50 mL) andconcentrated (3×) to ensure removal of excess trifluoroacetic acid. Theresulting white solid was dissolved in methanol (300 mL) and treatedwith DOWEX 550A-OH resin (approximately 120 g pre-washed with water andmethanol). After stirring the resin solution (pH 8.5) for 2 h, themixture was filtered and concentrated, re-dissolved in dichloromethaneand concentrated to give racemic(syn)-3-acetamido-4-allyl-N-(tert-butyl)pyrrolidine-3-carboxamide (IIaand IIb, 14.4 g, 99%) as a white foam. ¹H NMR (400 MHz, d₄MeOH) δ5.82-5.71 (m, 1H) 5.10-5.01 (m, 2H) 3.76 (d, J=11.9 Hz, 1H) 3.16 (dd,J=11.3, 7.6 Hz, 1H) 2.97 (d, J=11.9 Hz, 1H) 2.70 (dd, J=11.3, 7.1 Hz,1H) 2.40-2.35 (m, 1H) 2.32-2.24 (m, 1H) 1.98 (s, 3H) 1.92-1.84 (m, 1H)1.33 (s, 9H). FIG. 1 shows (IIa and IIb) by chiral HPLC.

Example 2 Preparation of (R)-2-((1-phenylethyl)carbamoyl)benzoic acid(3)

Synthesis of (R)-2-((1-phenylethyl)carbamoyl)benzoic acid (3). Asuspension of phthalic anhydride (50 g, 337.6 mmol) in EtOAc (200 mL)and THF (200 mL) was cooled to 5-10° C. with stirring and carefullytreated with (R)-(+)-1-phenylethylamine (47.37 mL, 371.3 mmol). Afterthe addition was complete the reaction became clear, the ice bath wasremoved and the solution stirred for 15 hours. The reaction mixture wasdiluted with ethyl acetate (200 mL), washed with 2N HCl, saturatedaqueous sodium chloride and water, dried over sodium sulfate, filtered,and concentrated under reduced pressure. The crude product wasrecrystallized from MTBE and hexanes to give(R)-2-((1-phenylethyl)carbamoyl)benzoic acid (3, 64.6 g, 71%) as a whitepowder. NMR (400 MHz, DMSO) δ 8.67 (d, J=8.2 Hz, 1H) 7.72 (dd, 1.3 Hz,1H) 7.53 (td, J=7.6, 1.4 Hz, 1H) 7.45 (td, J=7.6, 1.4 Hz, 1H) 7.38-7.35(m, 3H) 7.27 (t, J=7.6 Hz, 2H) 7.20-7.09 (m, 1H) 5.09-5.02 (m, 1H) 1.37(d, J=7.0 Hz, 3H).

Example 3 Preparation of(2S,3S)-2,3-bis(benzoyloxy)-4-(dimethylamino)-4-oxobutanoic acid (4)

Step 1: Synthesis of (3S,4S)-2,5-dioxotetrahydrofuran-3,4-diyldibenzoate

A suspension of (+)-2,3-dibenzoyl-D-tartaric acid (300 g, 358.3 mmol) inacetic anhydride (600 mL) was warmed to 85° C. with stirring. After 2 h,the solution was cooled in an ice bath and the resulting suspension wasfiltered, washed with 1:1 hexanes/diethyl ether (500 mL) and dried invacuo to afford (3S,4S)-2,5-dioxotetrahydrofuran-3,4-diyl dibenzoate(239 g, 84% yield) as a white crystalline solid. NMR (400 MHz, CDCl₃) δ8.08-8.06 (m, 4H) 7.67-7.63 (m, 2H) 7.51-7.47 (m, 4H) 5.98 (s, 2H).

Step 2: Synthesis of(2S,3S)-2,3-bis(benzoyloxy)-4-(dimethylamino)-4-oxobutanoic acid

A solution of (3S,4S)-2,5-dioxotetrahydrofuran-3,4-diyl dibenzoate (90g, 264.5 mmol) in ethyl acetate (150 mL) was cooled to 0° C. andcarefully treated with 2M dimethylamine in THF (158.7 mL, 317.4 mmol).Once the addition was complete, the ice bath was removed and thesolution stirred for an additional 2 h, then sequentially washed with 2N HCl, saturated aqueous sodium chloride, dried over sodium sulfate,filtered and concentrated. The crude product was recrystallized fromMTBE and hexanes to give(2S,3S)-2,3-bis(benzoyloxy)-4-(dimethylamino)-4-oxobutanoic acid (4, 81g, 79% yield) as a white powder. NMR (400 MHz, CDCl₃) δ 8.04-8.00 (m,4H) 7.56-7.52 (m, 2H) 7.42-7.37 (m, 4H) 6.22 (d, J=6.0 Hz, 1H) 5.95 (d,J=6.0 Hz, 1H) 3.18 (s, 3H) 2.97 (s, 3H).

Example 4 Preparation of(2S,3S)-2,3-bis(benzoyloxy)-4-(diethylamino)-4-oxobutanoic acid

While under nitrogen, a suspension of(3S,4S)-2,5-dioxotetrahydrofuran-3,4-diyl dibenzoate (1.021 g, 3.0 mmol)in anhydrous THF (15 mL) was cooled in an ice bath, and treated withdiethylamine (0.6 mL, 5.8 mmol). Once the addition was complete, themixture was allowed to warm to room temperature over 1 h, with continuedstirring for 16 h. The solution was treated with DOWEX 50W-X8 acid resin(3 g, prewashed with methanol), stirred a few minutes, filtered and thefiltrate concentrated. The residual oil was dissolved in ethyl acetate(10 mL) and hexane (20 mL) while stirring. After stirring for 15 min,the resulting suspension was cooled in an ice-bath for 15 min, filteredand rinsed with 3:1 hexane/ethyl acetate. The solid was dried to afford(2S,3S)-2,3-bis(benzoyloxy)-4-(diethylamino)-4-oxobutanoic acid (5, 896mg, 72% yield) as a white powder. NMR (400 MHz, CDCl₃) δ 8.04-7.99 (m,4H) 7.55-7.50 (m, 2H) 7.40-7.36 (m, 4H) 6.19 (d, J=5.9 Hz, 1H) 5.95 (d,J=5.9 Hz, 1H) 3.55-3.44 (m, 3H) 3.27-3.18 (m, 1H) 1.23 (t, J=7.1 Hz, 3H)1.05 (t, J=7.1 Hz, 3H).

Example 5 Preparation of(2S,3S)-2,3-bis(benzoyloxy)-4-oxo-4-(pyrrolidin-1-yl)butanoic acid

While under nitrogen, a suspension of(3S,4S)-2,5-dioxotetrahydrofuran-3,4-diyl dibenzoate (2.04 g, 6.0 mmol)in anhydrous THF (30 mL) was cooled in an ice bath, and treated withpyrrolidine (0.96 mL, 11.7 mmol). Once the addition was complete, themixture was allowed to warm to room temperature over 1 h, with continuedstirring for 16 h. The solution was treated with DOWEX 50W-X8 acid resin(6 g, prewashed with methanol), stirred a few minutes, filtered and thefiltrate concentrated. The residual oil was dissolved in dichloromethaneand loaded onto a silica gel column (˜100 cc) and eluted sequentiallywith ethyl acetate, 10% methanol in ethyl acetate, and 88:12:2 ethylacetate/methanol/acetic acid to afford(2S,3S)-2,3-bis(benzoyloxy)-4-oxo-4-(pyrrolidin-1-yl)butanoic acid (6,1.94 g, 79% yield) as a white foam. NMR (400 MHz, CDCl3) δ 8.05-8.00 (m,4H) 7.57-7.53 (m, 2H) 7.42-7.38 (m, 4H) 6.06 (dd, J=6.4 Hz, 1H) 5.94(dd, J=6.3 Hz, 1H) 3.82-3.76 (m, 1H) 3.57-3.51 (m, 2H) 3.46-3.40 (m, 1H)1.97-1.72 (m, 4H).

Example 6 Preparation of(2S,3S)-2,3-bis(benzoyloxy)-4-(isopropylamino)-4-oxobutanoic acid

A solution of (3S,4S)-2,5-dioxotetrahydrofuran-3,4-diyl dibenzoate (88g, 258.6 mmol) in ethyl acetate (132 mL) and THF (132 mL) was cooled to0° C. and carefully treated with 2-aminopropane (26.6 mL, 310.3 mmol).Once the addition was complete, the ice bath was removed and thesolution stirred for an additional 2 h, then sequentially washed with 2N HCl, saturated aqueous sodium chloride, dried over sodium sulfate,filtered and concentrated. The crude product was recrystallized fromMTBE and hexanes to give(2S,3S)-2,3-bis(benzoyloxy)-4-(isopropylamino)-4-oxobutanoic acid (7,97.4 g, 94% yield) as a white powder. NMR (400 MHz, CDCl₃) δ 8.05-8.01(m, 4H) 7.67-7.51 (m, 2H) 7.48-7.40 (m, 4H) 6.02 (d, J=3.4 Hz, 1H) 5.98(d, J=3.4 Hz, 1H) 4.12-4.04 (m, 1H) 1.09 (d, J=6.6 Hz, 3H) 1.06 (d,J=6.6 Hz, 3H).

Example 7 Preparation of(3S,4S)-5-(isopropylamino)-3,4-bis((4-methylbenzoyl)oxy)-2,5-dioxopentanoicacid (8)

Step 1: Synthesis of (3S,4S)-2,5-dioxotetrahydrofuran-3,4-diylbis(4-methylbenzoate)

A suspension of (+)-2,3-di-O-toluoyl-D-tartaric acid (15.0 g, 38.82mmol) in acetic anhydride (45 mL) was warmed to 85° C. with stirring.After 2 h, the solution was cooled in an ice bath and the resultingsuspension was filtered, washed with 1:1 hexanes/diethyl ether (100 mL)and dried in vacuo to afford (3 S,4S)-2,5-dioxotetrahydrofuran-3,4-diylbis(4-methylbenzoate) (10.85 g, 76%)as a white crystalline solid. NMR (400 MHz, CDCl₃) δ 7.95 (d, J=8.3 Hz,4H) 7.28 (d, J=8.3 Hz, 4H) 5.92 (s, 2H) 2.42 (s, 6H).

Step 2: Synthesis of (3 S,4S)-5-(isopropylamino)-3,4-bis((4-methylbenzoyl)oxy)-2,5-dioxopentanoicacid

A suspension of (3S,4S)-2,5-dioxotetrahydrofuran-3,4-diylbis(4-methylbenzoate) (5.0 g, 13.57 mmol) in ethyl acetate (20 mL) andTHF (20 mL) was cooled to 0° C. and treated with 2-aminopropane (1.40mL, 16.29 mmol). Upon addition the suspension became thick. The ice bathwas removed and stirring continued for an additional 1 h. Dichlormethane(100 mL) was added and the solution was sequentially washed with 2 NHCl, saturated aqueous sodium chloride, dried over sodium sulfate,filtered, and concentrated. The crude product was recrystallized fromMTBE and hexanes to give (3S,4S)-5-(isopropylamino)-3,4-bis((4-methylbenzoyl)oxy)-2,5-dioxopentanoicacid (8, 5.62 g, 97%) as a white powder. NMR (400 MHz, CDCl₃) δ7.94-7.90 (m, 4H) 7.25 (d, J=7.8 Hz, 2H) 7.21 (d, J=8.0 Hz, 2H) 5.99 (d,J=3.5 Hz, 1H) 5.95 (d, J=3.5 Hz, 1H) 4.12-4.03 (m, 1H) 2.41 (s, 3H) 2.39(s, 3H) 1.08 (d, J=6.6 Hz, 3H) 1.06 (d, J=6.5 Hz, 3H).

Example 8 Selective Crystallization of Racemic(syn)-3-acetamido-4-allyl-N-(tert-butyl)pyrrolidine-3-carboxamide (IIaand IIb) with (R)-2-((1-phenylethyl)carbamoyl)benzoic Acid (3)

A solution of racemic(syn)-3-acetamido-4-allyl-N-(tert-butyl)pyrrolidine-3-carboxamide (150mg, 0.5 mmol), (R)-2-((1-phenylethyl)carbamoyl)benzoic acid (83 mg, 0.55eq) and acetic acid (17 mg, 0.5 eq) in 25% methanol/ethyl acetate (18mL) was warmed until the solution became clear. After the solution wasallowed to cool to ambient temperature, the salt slowly crystalized fromthe solution. After about 48 h, the resulting crystalline material wasfiltered, washed with an ice-cooled solution of 25% methanol/ethylacetate and dried to give the enriched salt (34% yield, 99.7% ee). FIG.2 shows the salt of Example 8 by chiral HPLC.

Example 9 Selective Crystallization of Racemic(syn)-3-acetamido-4-allyl-N-(tert-butyl)pyrrolidine-3-carboxamide (IIaand IIb) with (R)-2-((1-phenylethyl)carbamoyl)benzoic acid (3)

A solution of racemic(syn)-3-acetamido-4-allyl-N-(tert-butyl)pyrrolidine-3-carboxamide (75mg, 0.28 mmol) and (R)-2-((1-phenylethyl)carbamoyl)benzoic acid (76 mg,0.28 eq) in 15% methanol/ethyl acetate (4 mL) was warmed until thesolution became clear. After the solution was allowed to cool to ambienttemperature, the salt slowly crystalized from the solution. After about24 h the resulting crystalline material was filtered, washed with anice-cooled solution of 15% methanol/ethyl acetate and dried to give theenriched salt (66% yield, 84.8% ee). FIG. 3 shows the salt of Example 9by chiral HPLC.

Example 10 Selective Crystallization of Racemic(syn)-3-acetamido-4-allyl-N-(tert-butyl)pyrrolidine-3-carboxamide (IIaand IIb) with(2S,3S)-2,3-bis(benzoyloxy)-4-(dimethylamino)-4-oxobutanoic acid (4)

A solution of racemic(syn)-3-acetamido-4-allyl-N-(tert-butyl)pyrrolidine-3-carboxamide (1.65g, 6.17 mmol) in methanol (9 mL) was treated with a second solution of(2S,3S)-2,3-bis(benzoyloxy)-4-(dimethylamino)-4-oxobutanoic acid (2.37g, 6.17 mmol) in warm isopropanol (41 mL). After the solutions werecombined and allowed to cool to ambient temperature, the salt slowlycrystalized from the solution (48-72 h). This resulting crystallinematerial was filtered, washed with an ice-cooled solution of 33%methanol/isopropanol and dried to give the enriched salt (77% yield,99.5% ee). FIG. 4 shows the salt of Example 10 by chiral HPLC.

Example 11 Selective Crystallization of Racemic(syn)-3-acetamido-4-allyl-N-(tert-butyl)pyrrolidine-3-carboxamide (IIaand IIb) with (2S,3S)-2,3-bis(benzoyloxy)-4-(diethylamino)-4-oxobutanoicacid (5)

A solution of racemic(syn)-3-acetamido-4-allyl-N-(tert-butyl)pyrrolidine-3-carboxamide (75mg, 0.28 mmol) and(2S,3S)-2,3-bis(benzoyloxy)-4-(diethylamino)-4-oxobutanoic acid (116 mg,0.28 mmol) in ethyl acetate (3 mL) was warmed until the solution becameclear. After the solution was allowed to cool to ambient temperature,the salt slowly crystalized from the solution. After about 24 h theresulting crystalline material was filtered, washed with ice cold ethylacetate and dried to give the enriched salt (84% yield, 45% ee). FIG. 5shows the salt of Example 11 by chiral HPLC.

Example 12 Selective Crystallization of Racemic(syn)-3-acetamido-4-allyl-N-(tert-butyl)pyrrolidine-3-carboxamide (IIaand IIb) with(2S,3S)-2,3-bis(benzoyloxy)-4-oxo-4-(pyrrolidin-1-yl)butanoic acid (6)

A solution of racemic(syn)-3-acetamido-4-allyl-N-(tert-butyl)pyrrolidine-3-carboxamide (75mg, 0.28 mmol) and(2S,3S)-2,3-bis(benzoyloxy)-4-oxo-4-(pyrrolidin-1-yl)butanoic acid (115mg, 0.28 mmol) in 15% methanol/ethyl acetate (4 mL) was warmed until thesolution became clear. After the solution was allowed to cool to ambienttemperature, the salt slowly crystalized from the solution. After about24 h the resulting crystalline material was filtered, washed with anice-cooled solution of 15% methanol/ethyl acetate and dried to give theenriched salt (73% yield, 95.4% ee). FIG. 6 shows the salt of Example 12by chiral HPLC.

Example 13 Selective Crystallization of Racemic(syn)-3-acetamido-4-allyl-N-(tert-butyl)pyrrolidine-3-carboxamide (IIaand IIb) with(2S,3S)-2,3-bis(benzoyloxy)-4-(isopropylamino)-4-oxobutanoic acid (7)

A solution of racemic(syn)-3-acetamido-4-allyl-N-(tert-butyl)pyrrolidine-3-carboxamide (1.65g, 6.17 mmol) in isopropanol (20 mL) was treated with a second solutionof (2S,3S)-2,3-bis(benzoyloxy)-4-(isopropylamino)-4-oxobutanoic acid(2.46 g, 6.17 mmol) in warm 55% methanol/isopropanol (30 mL). After thesolutions are combined and allowed to cool to ambient temperature, thedesired salt slowly crystallizes from the solution. After about 48 h theresulting crystalline material is filtered, washed with an ice-cooledsolution of 33% methanol/isopropanol and dried to give the enriched salt(77% yield, 99.7% ee). FIG. 7 shows the salt of Example 13 by chiralHPLC.

Example 14 Selective Crystallization of Racemic(syn)-3-acetamido-4-allyl-N-(tert-butyl)pyrrolidine-3-carboxamide (IIaand IIb) with(2S,3S)-2,3-bis(benzoyloxy)-4-(isopropylamino)-4-oxobutanoic acid (7)

A stirred solution of racemic(syn)-3-acetamido-4-allyl-N-(tert-butyl)pyrrolidine-3-carboxamide (0.83g 3.10 mmol) in isopropanol (10 mL) was treated with a second solutionof (2S,3S)-2,3-bis(benzoyloxy)-4-(isopropylamino)-4-oxobutanoic acid(1.24 g, 3.10 mmol) in warm 55% methanol/isopropanol (15 mL). Withcontinued stirring, the solutions are combined and allowed to cool toambient temperature. After about 24 h the resulting crystalline materialis filtered, washed with an ice-cooled solution of 33%methanol/isopropanol and dried to give the enriched salt (81% yield,97.8% ee). FIG. 8 shows the salt of Example 14 by chiral HPLC.

Example 15 Selective Crystallization of Racemic(syn)-3-acetamido-4-allyl-N-(tert-butyl)pyrrolidine-3-carboxamide (IIaand IIb) with(3S,4S)-5-(isopropylamino)-3,4-bis((4-methylbenzoyl)oxy)-2,5-dioxopentanoicacid (8)

A solution of racemic(syn)-3-acetamido-4-allyl-N-(tert-butyl)pyrrolidine-3-carboxamide (75mg, 0.28 mmol) and(3S,4S)-5-(isopropylamino)-3,4-bis((4-methylbenzoyl)oxy)-2,5-dioxopentanoicacid (120 mg, 0.28 mmol) in acetonitrile (1 mL) was warmed until thesolution became clear. After the solution was allowed to cool to ambienttemperature, the desired salt slowly crystallizes from the solution.After about 24 h the resulting crystalline material was filtered, washedwith ice cold acetonitrile and dried to give the enriched salt (46%yield, 96.4% ee). FIG. 9 shows the salt of Example 15 by chiral HPLC.

Example 16 General Method for the Preparation of Chiral (syn)tert-butyl-3-acetamido-4-allyl-3-(tert-butylcarbamoyl)pyrrolidine-1-carboxylatefrom the Selective Crystallizations (Examples 8-15)

A solution of the selectively crystalized salt (100 mg) in ethyl acetate(1 mL) and saturated aqueous NaHCO₃ (1 mL) is treated with di-tert-butyldicarbonate (1.5 equiv.). After stirring for 16-24 h, the organic layeris separated, filtered through a short pad of silica gel eluting with30% ethyl acetate/hexane then 100% ethyl acetate and concentrated togive (syn)tert-butyl-3-acetamido-4-allyl-3-(tert-butylcarbamoyl)pyrrolidine-1-carboxylateas a white solid that is analyzed by chiral HPLC.

Example 17 Chiral HPLC Method to Determine Enantiomeric Excess of (syn)tert-butyl-3-acetamido-4-allyl-3-(tert-butylcarbamoyl)pyrrolidine-1-carboxylate(IIa)

Samples are analyzed by HPLC using a Gilson 215 Liquid Handler equippedwith a PrepELS II Detector, Daicel Corporation Chiralpak IB 5 μm (4.6mm×250 mm) column using 10% ethanol/hexane, isocratic over 12 minuteswith a flow rate of 1 mL/min.

INCORPORATION BY REFERENCE

All publications and patents mentioned herein are hereby incorporated byreference in their entirety as if each individual publication or patentwas specifically and individually indicated to be incorporated byreference. In case of conflict, the present application, including anydefinitions herein, will control.

EQUIVALENTS

While specific embodiments of the present disclosure have beendiscussed, the above specification is illustrative and not restrictive.Many variations of the embodiments will become apparent to those skilledin the art upon review of this specification and the claims below. Thefull scope of the claimed invention should be determined by reference tothe claims, along with their full scope of equivalents, and thespecification, along with such variations.

The invention claimed is:
 1. An amine compound represented by formula I:

wherein: X is O, S, or NR^(e); R^(a) is H, lower alkyl, or lowercycloalkyl; R^(b) is —CH₂CH═CH₂, —CH₂CH₂CH₂Z¹, —(CH₂)_(n)C(O)H, or—(CH₂)_(n)CO₂Z²; R^(c) and R^(d) are independently H, lower alkyl, lowercycloalkyl, silyl, acyl, acyloxy; or R^(c) and R^(d), together with theN that links them, form an optionally substituted 3- to 6-memberedheteroaryl or heterocyclic ring; R^(c) is H or lower alkyl; n is 1 or 2;Z¹ is halogen, alkyl sulfonate, aryl sulfonate, or an alkyl sulfonateoptionally substituted with one or more halogen; and Z² is H, loweralkyl, or lower cycloalkyl; wherein the amine compound has anenantiomeric excess of greater than 75% ee.
 2. The amine compound ofclaim 1, wherein R^(a) is tert-butyl.
 3. The amine compound of claim 1,wherein R^(b) is —CH₂CH═CH₂.
 4. The amine compound of claim 1, whereinR^(c) is H.
 5. The amine compound of claim 1, wherein R^(d) is acetyl ortrifluoroacetyl.
 6. The amine compound of claim 1, wherein X is NH. 7.The amine compound of claim 1, wherein X is O.
 8. The amine compound ofclaim 1, wherein the amine compound is:

wherein R^(f) is H, lower alkyl, or lower cycloalkyl.
 9. The aminecompound of claim 1, wherein the amine compound has an enantiomericexcess of between 90% and 99.5% ee.
 10. The amine compound of claim 1,wherein the amine compound is:


11. The amine compound of claim 1, wherein the amine compound has anenantiomeric excess of greater than 97% ee.
 12. The amine compound ofclaim 8, wherein the amine compound has an enantiomeric excess ofbetween 90% and 99.5% ee.
 13. The amine compound of claim 8, wherein theamine compound has an enantiomeric excess of greater than 97% ee. 14.The amine compound of claim 8, wherein the amine compound has anenantiomeric excess of greater than 99% ee.
 15. The amine compound ofclaim 10, wherein the amine compound has an enantiomeric excess ofbetween 90% and 99.5% ee.
 16. The amine compound of claim 10, whereinthe amine compound has an enantiomeric excess of greater than 97% ee.17. The amine compound of claim 10, wherein the amine compound has anenantiomeric excess of greater than 99% ee.
 18. A process that uses theamine compound of claim 10 to prepare an arginase inhibitor of formulaIII:

wherein G is H, methyl, isopropyl, sec-butyl, —CH₂CH(CH₃)₂, benzyl,p-hydroxybenzyl, —CH₂OH, —CH(OH)CH₃, —CH₂-3-indoyl, —CH₂COOH,—CH₂CH₂COOH, —CH₂C(O)NH₂, —CH₂CH₂C(O)NH₂, —CH₂SH, —CH₂CH₂SCH₃,—(CH₂)₄NH₂, —(CH₂)₃NHC(═NH)NH₂, or —CH₂-3-imidazoyl; said processcomprising: (a) providing the amine compound of claim 10:

wherein the amine compound has an enantiomeric excess greater than 80%ee; (b) adding a protecting group to the secondary amine of the aminecompound provided in step (a) to form the following compound:

wherein the protecting group (Pg) is formyl, acetyl, trifluoroacetyl,benzyl, benzyloxycarbonyl, tert-butoxycarbonyl, trim ethyl silyl,2-trimethylsilyl-ethanesulfonyl, methoxymethyl, triethylsilyl,triisopropylsilyl, tert-butyldimethylsilyltrityl, trityl,allyloxycarbonyl, 9-fluorenylmethyloxycarbonyl, ornitro-veratryloxycarbonyl; (c) subjecting the compound prepared by step(b) to hydroboration conditions; (d) removing the secondary amineprotecting group from the compound prepared by step (c); (e) subjectingthe secondary amine of the compound prepared by step (d) to an amidationreaction; and (f) subjecting the compound prepared by step (e) toconditions sufficient to form the compound of formula III; wherein thecompound of formula III prepared by the process has an enantiomericexcess of greater than 80% ee.
 19. The process of claim 18, wherein theamine compound provided in step (a) has an enantiomeric excess greaterthan 90% ee.
 20. The process of claim 18, wherein the compound offormula III prepared by the process has an enantiomeric excess ofgreater than 90% ee.